Meiosis- lecture #14 Flashcards
chromosomes are present in what form?
homologous pairs
how many chromosomes are present in a human somatic cell?
46
each chromosome in the somatic cell has twin chromosome, that is identical in _______ and __________
length and centromere position
if you stain the chromosomes with dye what will happen? what will the chromosomes look like?
the matching chromosomes of a homologous pair display identical patterns that consist of stripes
in a female, in total a cell has how many chromosome pairs? what are these pairs called?
23 chromosome pairs
called homologous pairs
why are the chromosomes in these homologous pairings?
because they both contain genes that code for the same trait (hair color, eye color)
the location on a chromosome that a particular gene is found is called what?
the locus
how many homologous pairs does a male have?
22 homologous pairs and an XY chromosome
what do homologous pairs contain?
a gene encoding the same trait at the same locus
what can the homologous pairs encode?
a different version of the same gene
what is a karyotype?
visual display of homologous chromosomal pairs
how is a karyotype arranged?
beginning with the longest
how are the chromosomes viewed in a karyotype?
condensed and doubled
what phase of mitosis are karyotypes located?
metaphase of mitosis
what types of cells are used to prepare a karyotype?
white blood cells, specifically lymphocytes
what is done to the lymphocytes in order to begin mitosis?
they are chemically treated
why is another chemical added to the lymphocyte?
to arrest the cells in metaphase of mitosis
what is the exception to the homologous pair?
sex chromosomes
why are most genes carried on the X chromosome not have a counterpart on the Y chromosome?
the Y chromosome is much smaller than the X chromosome and will carry few genes of its own that cannot be found on the X chromosome
where is each chromosome from each homologous pair and one sex chromosome inherited from?
our mother and the other sex chromosome and the remaining member of the homologous pair is inherited from our father
somatic cells have how many chromosome pairs?
23
how many autosomes are in somatic cells?
22
what is the 23 chromosome pair?
sex chromosome pair
what needs to happen for our lifecycle to continue as we know it?
a sexually reproducing organism must have two chromosome sets
what is a cell with two sets of chromosomes called?
diploid cell
what is the diploid number abbreviated to?
2n
why are humans referred to as a diploid organisms?
the only cells in the human body that are not diploid are the gametes (sperm or egg)
what is a haploid cell?
a cell with only one set of chromosomes haploid number is n=23 in humans
what is an example of a haploid cell?
gametes
which parent chooses the gender? why?
father
they have X and Y
what is fertilization?
the fusion of two haploid gametes
one sperm and one egg
what does fertilization result in?
a zygote that now has 2 chromosome sets (diploid)
what would happen if gametes were not haploid?
fertilization would produce a tetraploid (4) organism, which is not sustainable for life
why is the human life cycle an alteration of diploid and haploid stages?
the zygote now has 46 chromosomes and divides by mitosis, which eventually produces a mature organism that produces its own haploid gametes
how are the haploid gametes produced?
by meiosis
where does meiosis occur?
ovaries and the testes
what does meiosis do to the chromosome number?
divides in half
46 –> 23
what does mitosis produce?
two daughter cells with the same chromosome number as the parent cell
overall what are the 4 steps of the sexual reproduction cycle?
diploid cells divide by meiosis to form haploid cells
haploid cells from two individuals fuse in pairs at fertilization
forms new diploid cells.
what are the 3 different sexual life cycles that exist?
human/animal life cycle
plant/algae life cycle
fungal life cycle
in the human/ animal life cycle where does meiosis take place? what does it produce?
germ cells
produces gametes
in the human/animal life cycle what does fertilization produce?
diploid zygote
what happens in the human/animal life cycle once the diploid zygote is produced?
divides by mitosis (to produce a multi-cellular organism)
in the plant/algae life cycle what type of multicellular stages does it consist of?
haploid (n) and diploid (2n) multi-cellular stages
in the plant/algae life cycle in the multicellular diploid phase what does the 2n sporophyte produce?
produces n spores by meiosis
what happens to the n spore in mitosis in the plant/algae life cycle?
n spore divides by mitosis
after the n spore divides in the plant/algae life cycle what is produced?
a haploid multicellular organism called a gametophyte
what does the gametophyte phase produce in the plant/algae life cycle?
n gametes by mitosis (another n gets inserted creating a 2n)
gametes in the plant/algae life cycle fuse producing a 2n zygote, what happens to the zygote next?
zygote divides by mitosis to produce a multicellular sporophyte phase (back to the beginning of the cycle)
in the fungal life cycle gametes fuse to produce what?
2n zygote
what happens to the zygote in the fungal life cycle?
zygote divides by meiosis producing n cells
what happens to the n cells next in the fungal life cycle?
n cells divide by mitosis to produce the n multicellular adult
in order to produce gametes what happens to the cells of the adult phase in the fungal life cycle?
divide by mitosis
single celled zygote is the only ___ phase in the fungal life cycle
2n
what does meiosis produce?
haploid cells
what are both mitosis and meiosis preceded by?
the doubling of each chromosome in the cell
how many cell divisions does mitosis have? what does it result in?
one cell division
results in two daughter cells
how many cell divisions does meiosis have? what does it result in?
two cell divisions
results in 4 daughter cells
meiosis produces daughter cells with only ___ the number of chromosomes as the parent cell
half
what are the main stages of meiosis?
meiosis I and meiosis II
out of the 4 daughter cells how many would be an egg? how many would be a sperm?
1/4 would be an egg
4/4 would be a sperm
before a cell enters meiosis I what phase does it go through?
interphase (the same way as in mitosis)
what does interphase do?
duplicates the chromosomes and the organelles present inside of the cell
what happens to the size of the cell in interphase?
doubles in size
what are the phases of interphase?
G1, S and G2
what are the phases of meiosis I?
prophase I
metaphase I
anaphase I
telophase I (may be incomplete)
Cytokinesis I
what is the most complex phase of the meiotic process?
prophase I of meiosis I
what happens to the chromatin in prophase I?
chromatin coils (becomes visible as chromosomes under the microscope
what disappears in prophase I?
nuclear membrane and the nucleolus
what forms in prophase I?
spindle apparatus forms
in prophase I, a process called synapsis occurs, what happens in that process?
homologous chromosome pairs line up beside one another ‘single file’
how are the homologues present in synapsis?
they are present in duplicate containing two sister chromatids
what is the structure that results from synapsis called?
tetrad (4)
what does a tetrad consist of?
4 chromatids
During prophase I what is responsible for producing genetic variation?
crossing over
what is crossing over?
after synapsis, chromatids of homologous pairs exchange pieces of chromosomes
why is this variation produced?
the homologues can carry alternate versions of a gene
for example, one homologue encodes brown hair and the other encodes blonde hair, what would happen during crossing over?
homologue encoding brown hair may now encode blonde hair or
homologue encoding blonde hair may now encode brown hair
do the chromatids contain other genes then hair color?
yes! therefore crossing over has created a different combination of gene types on the same chromatid
how are the chromosome tetrads aligned in metaphase?
aligned at the metaphase plate down the center of the cell
in metaphase sister chromatids remain attached to one another by their ______
centromeres
what are the spindle microtubules attached to in metaphase?
spindle microtubules are attached to the centromeres in preparation for cell division
explain how spindle microtubules are attached to this tetrad and how the homologous pairs are attached to one another
spindle microtubules from one pole of the cell are attached to one homologue
spindle microtubules from the other pole are attached to the other homologue
homologous pairs are held together by the sites of crossing over
what occurs during anaphase I?
homologous pairs separate from one another and move to opposite poles of the cell
are the sister chromatids still attached in anaphase I?
yes, by the centromere
during telophase I where are the chromosomes?
at opposite poles of the cell
each pole of the cell now has a _____ chromosome set in telophase I
haploid
each pole now has how many distinct chromosomes in telophase I
23
each of these 23 chromosomes in telophase I still contains ___ ______ _________
two sister chromatids
why is telophase likely to be incomplete in telophase I?
because we still have to go through meiosis II
analogy: you wouldn’t build a fence then take it down 10 minutes later, then put it back up again
why does cytokinesis occur at the same time as telophase?
more efficient, multitask
what happens in cytokinesis?
cytoplasm and its contents are divided into two and the haploid daughter cells are formed
during cytokinesis what may happen to the chromosomes?
may briefly uncoil and become active
does cytokinesis always occur in meiosis I?
no
in most cases the cell immediately proceeds into prophase II of meiosis II
is there an interphase II after meiosis I?
no, chromosomal duplication does not take place and therefore there is no additional cycle of interphase
in prophase II if chromosomes resume activity since meiosis I, what will happen to them?
then they will uncoil once again during prophase II
what does the spindle apparatus do in prophase II?
attach to the centromere of each duplicated chromosome
how does the spindle apparatus attach to the chromosomes?
attach to opposite side of the same chromosome so that sister chromatids can later be pulled apart
how are the chromosomes aligned in metaphase II?
down the metaphase plate
how many duplicated chromosomes are in a line down the center of the cell in metaphase II?
23
what happens to the sister chromatids in anaphase II?
move toward opposite poles of the cell
what happens to the centromeres in anaphase II?
separate
what reforms in telophase II?
nuclear membrane and nucleolus reform
what happens to chromosomes in telophase II?
chromosomes uncoil
what simultaneously occurs during telophase II?
cytokinesis
what is produced in cytokinesis II?
4 haploid daughter cells are formed from the initial parent cell that entered into meiosis I
what is mitosis used for?
growth, repair and asexual reproduction
what is meiosis used for?
sexual reproduction
what is the difference between daughter cells in mitosis and meiosis?
mitosis: daughter cells are diploid and genetically identical to the parent cell
meiosis: daughter cells are haploid and genetically distinct from the parent cell
what does mitosis and meiosis have in common?
both use chromosomal duplication before starting their processes (interphase)
is meiosis II identical to mitosis? why or why not?
essentially identical to mitosis except that cells entering meiosis II are haploid
what are the 3 origins of genetic variation?
independent chromosomal orientation
random fertilization
crossing over
what is independent chromosomal orientation?
shuffling of chromosomes
are the chromosomes inherited from your mother different then from your father?
yes,
the mother will often carry different versions of genes than the chromosomes that are inherited from to father
during tetrad formation what is the chance that the chromosome of maternal origin will end up on one side of the cell over the other?
50/ 50 chance
human sperm and human egg make up around how many possibilities?
64 trillion
how does random fertilization affect genetic variation?
any gamete can be used during fertilization
alternate gene alleles differentiate gametes from one another and give rise to genetic variation
when does crossing over occur?
during prophase I of meiosis I
what is the point of crossing over called?
chiasma
the part where two non-sister chromatids attach to one another
during crossing over each gene on one homologue is aligned with what?
precisely aligned with the same gene on the other homologue
what are new chromosome combinations called?
recombinants
in humans how many crossing over events occur per chromosome (per meiotic division)?
1-3 crossing over events
